This invention relates in general to vehicle steering shaft assemblies having two or more universal joints connected together. More specifically, this invention relates to a fixture for clearly and uniformly identifying the phase angle relationship between two universal joints in such a vehicle steering shaft assembly.
In virtually every road and off-road vehicle in use today, a steering system is provided for permitting a driver to control the direction of movement. A typical steering system includes a steering wheel and column assembly, an intermediate steering shaft assembly, and a steering device. The steering wheel is rotatably supported within a driver compartment of the vehicle for movement by the driver. The steering shaft assembly is connected to the steering wheel for rotation therewith. The steering device is connected to the steering shaft assembly for turning the wheels of the vehicle in response to rotation of the steering wheel.
In many larger vehicles, such as tracks, the steering shaft assembly is often designed not only to provide a rotational driving connection between the steering wheel and the steering device, but also to permit relative axial movement therebetween. Such axial movement has been found to be advantageous for two reasons. First, a relatively small amount of such axial movement is desirable to accommodate vibrations, bumps, and other aspects of normal vehicle operation which would otherwise be transmitted to the steering wheel. Second, when the vehicle is serviced, a relatively large mount of such axial movement is desirable to permit the cab of the vehicle to be pivoted upwardly without requiring disassembly of the steering system.
To accomplish this, it is known to construct the steering shaft assembly from cooperating male and female splined telescoping steering shaft members. The first steering shaft member is connected to the steering wheel by a first universal joint, while the second steering shaft member is connected to the steering device by a second universal joint. The universal joints are provided to permit angular displacement between the rotational axes of the steering shaft members and, therefore, the steering wheel and steering device associated therewith. The splined connection between the first and second steering shaft members provides a rotatable driving connection between the steering wheel and the steering device, while permitting relative axial movement therebetween.
Generally, the universal joints used in steering shaft assemblies are Cardan type universal joints. A typical Cardan type universal joint includes a pair of yokes which are interconnected by a cross. The cross includes a central body portion having four cylindrical trunnions extending outwardly therefrom. The trunnions are oriented in a single plane and extend at right angles relative to one another. A hollow cylindrical beating cup having a closed end is mounted on the end of each of the trunnions. A plurality of bearings, such as roller bearings or needle bearings, are provided between the outer cylindrical surface of a given trunnion and the inner cylindrical surface of the associated bearing cup to permit relative rotational movement therebetween. To form a Cardan type universal joint, a first yoke is connected to a first opposed pair of the bearing cups of the cross, while a second yoke is connected to a second opposed pair of the bearing cups. In the context of a steering shaft assembly, therefore, the first universal joint includes a first yoke secured to the end of the first steering shaft member and connected to the bearing cups mounted on the first opposed pair of the trunnions. The bearing cups mounted on the second opposed pair of the trunnions are connected by a second yoke for rotation with the steering wheel. Similarly, the second universal joint of the steering shaft assembly includes a first yoke secured to the end of the second steering shaft member and connected to the bearing cups mounted on the first opposed pair of the trunnions. The bearing cups mounted on the second opposed pair of the trunnions are connected by a second yoke for rotation with the steering device.
It is known that whenever a Cardan type universal joint is operated while the rotational axes of the two yokes are not aligned, non-uniform motion is developed. In other words, when one yoke (the driving yoke) is rotated an incremental angular distance, the other yoke (the driven yoke) does not rotate the same incremental angular distance. Rather, the driven yoke rotates either more or less than the incremental angular distance, depending upon the initial angular orientation. Similarly, when the driving yoke is rotated at a constant rotational velocity, the driven yoke does not rotate at the same constant rotational velocity. Rather, the driven yoke rotates either faster or slower than the rotational velocity, again depending upon the initial angular orientation. It has been found that the incremental angular displacement and velocity of the driven yoke vary in a sinusoidal manner relative to the constant angular displacement and velocity of the driven yoke. Thus, although the average angular displacement and velocity over one complete revolution of the driving and driven yokes is uniform, the incremental angular displacement and velocity within a complete revolution are not.
The consequence of these sinusoidal variations in angular displacement and velocity in a vehicle steering system is that undesirable torsional vibrations may be generated in the steering shaft assembly when the steering wheel is rotated to effect a turn. These torsional vibrations can be somewhat annoying to a driver of the vehicle and, therefore, are undesirable. The magnitude of these torsional vibrations is proportional to the square oft he operating angle of the universal joint. In steering systems and other devices where multiple universal joints are connected in series, the effects of universal joints may be combined and expressed as a single equivalent operating angle. Thus, the magnitude of the torsional vibrations in a multiple universal joint system is proportional to the square of the equivalent operating angle of the system.
To a certain extent, the torsional vibrations in a multiple universal joint system can be minimized if the two universal joints connected to the steering shaft assembly are properly oriented relative to one another. The relative angular orientation of the inboard yokes which are secured to the two ends of the steering shaft assembly is referred to as the phase angle. For example, let it be assumed that the inboard yokes of the two universal joints are aligned with one another (i.e., the axes of rotation defined by the respective pairs of cross bores formed through the associated yoke arms are parallel). This arrangement is referred to as a zero phase angle between the two universal joints. Further, let it be assumed that the plane defined by the first outboard yoke and the steering shaft assembly is common with the plane defined by the second outboard yoke and the steering shaft assembly. Lastly, let it be assumed that the outboard yokes extend at operating angles relative to the steering shaft assembly which are equal and opposite to one another. In this instance, the equivalent operating angle of the system is zero because the torsional vibrations generated by the first universal joint are equal and opposite (i.e., 180.degree. out of phase) to the torsional vibrations generated by the second universal joint. As a result, the torsional vibrations generated by the first universal joint are substantially canceled by the equal and opposite torsional vibrations generated by the second universal joint.
Unfortunately, the design of the vehicle in which the steering shaft assembly is installed dictates the directions in which the outboard yokes extend from the steering shaft assembly. Frequently, the outboard yokes do not extend in a common plane or at angles which are equal and opposite to one another. On the contrary, it is common not only that the two outboard yokes extend in different planes, but also that they extend at different operating angles. To accommodate this structure, while still providing some mutual cancellation of the undesired torsional vibrations, it is known to orient the two inboard yokes of the two universal joints at a non-zero phase angle (i.e., the axes defined by the respective pairs of cross bores are not parallel). This angular misalignment provides, in many instances, sufficient mutual cancellation of the sinusoidal variations to eliminate the annoying torsional vibrations during normal use.
One problem which has been encountered in the design and manufacture of vehicle steering shaft assemblies is that it is sometimes difficult to interpret what the desired phase angle relationship is from drawings which have been generated to illustrate the structure of the steering shaft assembly. In some instances, the standards used by a vehicle manufacturer may be different from the standards used by the supplier of the steering shaft assembly. In other instances, the standards used by the designer of the steering shaft assembly may be different from the manufacturer of the steering shaft assembly. Because of these difficulties, it would be desirable to provide a fixture which clearly and unambiguously identifies the phase angle relationships between the universal joints secured to the ends of a steering shaft assembly.